A Tightly Coupled Inductive Power Transfer System for Low-Voltage and High-Current Charging of Automatic Guided Vehicles

Abstract

This paper proposes a tightly coupled inductive power transfer (IPT) system for the low-voltage and high-current charging of automatic guided vehicles (AGVs). There are two challenges in the system design. First, the widely varying range of the airgap introduces difficulties to design the compensation circuit. Second, the low-voltage and high-current working condition introduces difficulties to maintain the system efficiency. This paper reveals that there are a large amount of high-order harmonic currents in a tightly coupled IPT system, and we have provided an effective design method to reduce the harmonics. The integrated LCC compensation circuit is selected as a solution, showing four merits: good robustness to the airgap variation, easy controllability, convenience to optimize the efficiency, and low high-order harmonics. A prototype is implemented, and the magnetic coupler size is 220 × 200 × 10 mm. Experimental results show that it achieves 1.78 kW power transfer from a 300 V dc source to a 24 V battery with 86.1% efficiency and a 73.8 A charging current across an airgap of 15 mm. When the airgap varies between 5 and 25 mm, the system power variation is within ±36.7% and the efficiency is not significantly affected.